Did Norsemen, coming via Greenland and, perhaps, Hudson Bay, penetrate the Minnesota-Great Lakes area over a century before Columbus? A number of students and fervent Scandinavian-Americans, their belief fortified by scraps of Norse legend and literature and supported by such supposed relics as the Kensington rune stone, are sure of it. Most scholars, however, either doubt or reject the story, and their chief spokesman is Erik Wahlgren, professor of Scandinavian languages at the University of California at Los Angeles.